The present invention relates to hydrodynamic fluid film bearing systems.
Hydrodynamic fluid film journal bearings, also called journal air bearings or foil bearings, can be used to provide support to rotatable components such as shafts. A typical prior art bearing assembly of this type (e.g., as disclosed by U.S. Pat. No. 5,658,079), includes a journal sleeve, a bump foil, an intermediate foil, and a top foil. The bump foil, the intermediate foil and the top foil are wrapped inside the journal sleeve in a substantially cylindrical shape, and those foils are positioned between the journal sleeve and the rotatable component. Each foil has an end that is engaged to the journal sleeve, and can have another end that is free (i.e., not engaged to the journal sleeve). During operation, rotation of the rotatable component causes a working fluid to form a cushion (often referred to as an “air bearing”) that supports the rotatable component with little or no direct contact between the rotatable component and the foils of the bearing.
Conventional hydrodynamic fluid film journal bearings have a substantially cylindrical journal sleeve. These cylindrical journal sleeves have walls of uniform thickness defined between an outer diameter surface and an opposite inner diameter surface. Those journal sleeve walls are relatively thick for providing stiffness. However, such thick journal sleeve walls add considerable weight to the bearing. Weight of bearings is an important design consideration, particularly for aerospace applications.